Protection mechanisms for multi-user MIMO transmissions

ABSTRACT

Certain aspects of the present disclosure relate to techniques for medium reservation in the case of multi-user (MU) communications. Multiple mechanisms are supported for protecting MU transmissions, wherein appropriate control messages can be exchanged between an access point and served user stations before transmitting downlink data packets.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

The present Application for Patent claims benefit of U.S. ProvisionalPatent Application Ser. No. 61/319,686, filed Mar. 31, 2010, and U.S.Provisional Patent Application Ser. No. 61/345,004, filed May 14, 2010and assigned to the assignee hereof and hereby expressly incorporated byreference herein.

CROSS REFERENCE TO RELATED APPLICATIONS

The present Application for Patent is related by subject matter to U.S.patent application Ser. No. 13/076,031 and U.S. patent application Ser.No. 13/076,114, filed herewith and assigned to the assignee hereof andhereby expressly incorporated by reference herein.

BACKGROUND

1. Field

Certain aspects of the present disclosure generally relate to wirelesscommunications and, more particularly, to methods and apparatus formedium reservation in the case of multi-user transmissions.

2. Background

In order to address the issue of increasing bandwidth requirements thatare demanded for wireless communications systems, different schemes arebeing developed to allow multiple user terminals to communicate with asingle access point by sharing the channel resources while achievinghigh data throughputs. Multiple Input Multiple Output (MIMO) technologyrepresents one such approach that has recently emerged as a populartechnique for the next generation communication systems. MIMO technologyhas been adopted in several emerging wireless communications standardssuch as the Institute of Electrical and Electronics Engineers (IEEE)802.11 standard. The IEEE 802.11 denotes a set of Wireless Local AreaNetwork (WLAN) air interface standards developed by the IEEE 802.11committee for short-range communications (e.g., tens of meters to a fewhundred meters).

The IEEE 802.11 WLAN standards body established specifications fortransmissions based on the very high throughput (VHT) approach using acarrier frequency of 5 GHz (i.e., the IEEE 802.11ac specification), orusing a carrier frequency of 60 GHz (i.e., the IEEE 802.11adspecification) targeting aggregate throughputs larger than 1 Gigabitsper second. One of the enabling technologies for the VHT 5 GHzspecification is a wider channel bandwidth, which bonds two 40 MHzchannels for 80 MHz bandwidth therefore doubling the physical layer(PHY) data rate with negligible increase in cost compared to the IEEE802.11n standard.

A MIMO system employs multiple (N_(T)) transmit antennas and multiple(N_(R)) receive antennas for data transmission. A MIMO channel formed bythe N_(T) transmit and N_(R) receive antennas may be decomposed intoN_(S) independent channels, which are also referred to as spatialchannels, where N_(S) ≦min {N_(T), N_(R)}. Each of the N_(S) independentchannels corresponds to a dimension. The MIMO system can provideimproved performance (e.g., higher throughput and/or greaterreliability) if the additional dimensionalities created by the multipletransmit and receive antennas are utilized.

In IEEE 802.11 networks, transmissions can occur by following a randommedium access mechanism called Carrier Sense Multiple Access withCollision Avoidance (CSMA/CA). Transmissions from one node can happenconcurrently with transmissions from other nodes in the network, andthis situation can be referred to as a collision. The CSMA/CA mechanismtries to avoid collisions by having nodes (i.e., user stations (STAs))sense the medium before starting a transmission in order to ensure thatno other STA is already transmitting. In some configurations, not allthe STAs are able to hear each other, and the sensing mechanism canfail. This can be referred to as the hidden node scenario. In order tolimit the latter case, the concept of Network Allocation Vector (NAV) ispresent in the IEEE 802.11 standard, wherein NAV information maycomprise an indication of time for which the medium is going to be busy.This indication may be relied to the hidden nodes by using appropriatemessages.

The IEEE 802.11 standard specifies the use ofRequest-to-send/Clear-to-send (RTS/CTS) messages to provide the NAVinformation to hidden node(s), and hence provide protection for theimmediately following transmission. The RTS/CTS mechanism can be alsouseful in lowering the overhead caused by collisions. If an RTS messageis transmitted before the data and a collision happens, then the CTSmessage will be missing, which allows to identify the collision event.Also the RTS message is typically much shorter message than data, andhence the time taken by the collision is short.

The RTS/CTS mechanism can also allow detecting the NAV being set byneighboring networks, which may be hidden to the transmitter. If a CTSmessage is not received, the reason can be that the NAV for the RTSreceiver was set, preventing the RTS receiver to reply with a CTSmessage.

A Multi-User MIMO (MU-MIMO) transmission in IEEE 802.11 networks maycomprise data destined to multiple STAs scheduled for simultaneoustransmission. In this case, efficient protection of the MU-MIMOtransmission is desired.

SUMMARY

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes a transmitterconfigured to transmit one or more reservation messages, each of the oneor more reservation messages being destined to a different apparatus ofa plurality of apparatuses to reserve a medium for data communication,and a receiver configured to receive one or more confirmation messages,each of the one or more confirmation messages was transmitted from thedifferent apparatus in response to that reservation message, wherein thetransmitter is also configured to transmit, in response to the one ormore confirmation messages, data over the medium to the apparatuses.

Certain aspects of the present disclosure provide a method for wirelesscommunications. The method generally includes transmitting one or morereservation messages, each of the one or more reservation messages beingdestined to a different apparatus of a plurality of apparatuses toreserve a medium for data communication, receiving one or moreconfirmation messages, each of the one or more confirmation messages wastransmitted from the different apparatus in response to that reservationmessage, and transmitting, in response to the one or more confirmationmessages, data over the medium to the apparatuses.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means fortransmitting one or more reservation messages, each of the one or morereservation messages being destined to a different apparatus of aplurality of apparatuses to reserve a medium for data communication, andmeans for receiving one or more confirmation messages, each of the oneor more confirmation messages was transmitted from the differentapparatus in response to that reservation message, wherein the means fortransmitting is further configured to transmit, in response to the oneor more confirmation messages, data over the medium to the apparatuses.

Certain aspects of the present disclosure provide a computer-programproduct for wireless communications. The computer-program productincludes a computer-readable medium comprising instructions executableto transmit one or more reservation messages, each of the one or morereservation messages being destined to a different apparatus of aplurality of apparatuses to reserve a medium for data communication,receive one or more confirmation messages, each of the one or moreconfirmation messages was transmitted from the different apparatus inresponse to that reservation message, and transmit, in response to theone or more confirmation messages, data over the medium to theapparatuses.

Certain aspects of the present disclosure provide an access point. Theaccess point generally includes at least one antenna, a transmitterconfigured to transmit one or more reservation messages via the at leastone antenna, each of the one or more reservation messages being destinedto a different access terminal of a plurality of access terminals toreserve a medium for data communication, and a receiver configured toreceive one or more confirmation messages via the at least one antenna,each of the one or more confirmation messages was transmitted from thedifferent access terminal in response to that reservation message,wherein the transmitter is also configured to transmit, via the at leastone antenna in response to the one or more confirmation messages, dataover the medium to the access terminals.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes a receiverconfigured to receive, at the apparatus of a plurality of apparatuses, areservation message from one or more reservation messages, each of theone or more reservation messages being destined to a different one ofthe apparatuses for reserving a medium for data communication, and atransmitter configured to transmit a confirmation message in response tothe reservation message, wherein the receiver is also configured toreceive data dedicated to the apparatus, the data being transmitted overthe medium.

Certain aspects of the present disclosure provide a method for wirelesscommunications. The method generally includes receiving, at an apparatusof a plurality of apparatuses, a reservation message from one or morereservation messages, each of the one or more reservation messages beingdestined to a different one of the apparatuses for reserving a mediumfor data communication, transmitting a confirmation message in responseto the reservation message; and receiving data dedicated to theapparatus, the data being transmitted over the medium.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means forreceiving, at the apparatus of a plurality of apparatuses, a reservationmessage from one or more reservation messages, each of the one or morereservation messages being destined to a different one of theapparatuses for reserving a medium for data communication, and means fortransmitting a confirmation message in response to the reservationmessage, wherein the means for receiving is further configured toreceive data dedicated to the apparatus, the data being transmitted overthe medium.

Certain aspects of the present disclosure provide a computer-programproduct for wireless communications. The computer-program productincludes a computer-readable medium comprising instructions executableto receive, at an apparatus of a plurality of apparatuses, a reservationmessage from one or more reservation messages, each of the one or morereservation messages being destined to a different one of theapparatuses for reserving a medium for data communication, transmit aconfirmation message in response to the reservation message, and receivedata dedicated to the apparatus, the data being transmitted over themedium.

Certain aspects of the present disclosure provide an access terminal.The access terminal generally includes at least one antenna, a receiverconfigured to receive, at the access terminal of a plurality of accessterminals via the at least one antenna, a reservation message from oneor more reservation messages, each of the one or more reservationmessages being destined to a different one of the access terminals forreserving a medium for data communication, and a transmitter configuredto transmit, via the at least one antenna, a confirmation message inresponse to the reservation message, wherein the receiver is alsoconfigured to receive data dedicated to the access terminal via the atleast one antenna, the data being transmitted over the medium.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to aspects, some ofwhich are illustrated in the appended drawings. It is to be noted,however, that the appended drawings illustrate only certain typicalaspects of this disclosure and are therefore not to be consideredlimiting of its scope, for the description may admit to other equallyeffective aspects.

FIG. 1 illustrates an example wireless communications network inaccordance with certain aspects of the present disclosure.

FIG. 2 illustrates a block diagram of an example access point and userterminals in accordance with certain aspects of the present disclosure.

FIG. 3 illustrates a block diagram of an example wireless device inaccordance with certain aspects of the present disclosure.

FIG. 4 illustrates a first example exchange of control messagespreceding multiuser multiple-input multiple-output (MU-MIMO)transmission in accordance with certain aspects of the presentdisclosure.

FIG. 5 illustrates first example operations that may be performed at anaccess point in accordance with certain aspects of the presentdisclosure.

FIG. 5A illustrates example components capable of performing theoperations illustrated in FIG. 5.

FIG. 6 illustrates first example operations that may be performed at auser station in accordance with certain aspects of the presentdisclosure.

FIG. 6A illustrates example components capable of performing theoperations illustrated in FIG. 6.

FIG. 7 illustrates a second example exchange of control messagespreceding MU-MIMO transmission in accordance with certain aspects of thepresent disclosure.

FIG. 8 illustrates second example operations that may be performed at anaccess point in accordance with certain aspects of the presentdisclosure.

FIG. 8A illustrates example components capable of performing theoperations illustrated in FIG. 8.

FIG. 9 illustrates second example operations that may be performed at auser station in accordance with certain aspects of the presentdisclosure.

FIG. 9A illustrates example components capable of performing theoperations illustrated in FIG. 9.

FIG. 10 illustrates a third example exchange of control messagespreceding MU-MIMO transmission in accordance with certain aspects of thepresent disclosure.

FIG. 11 illustrates a fourth example exchange of control messagespreceding MU-MIMO transmission in accordance with certain aspects of thepresent disclosure.

FIG. 12 illustrates a fifth example exchange of control messagespreceding MU-MIMO transmission in accordance with certain aspects of thepresent disclosure.

FIG. 13 illustrates third example operations that may be performed at anaccess point in accordance with certain aspects of the presentdisclosure.

FIG. 13A illustrates example components capable of performing theoperations illustrated in FIG. 13.

FIG. 14 illustrates third example operations that may be performed at auser station in accordance with certain aspects of the presentdisclosure.

FIG. 14A illustrates example components capable of performing theoperations illustrated in FIG. 14.

DETAILED DESCRIPTION

Various aspects of certain aspects of the present disclosure aredescribed below. It should be apparent that the teachings herein may beembodied in a wide variety of forms and that any specific structure,function, or both being disclosed herein is merely representative. Basedon the teachings herein one skilled in the art should appreciate that anaspect disclosed herein may be implemented independently of any otheraspects and that two or more of these aspects may be combined in variousways. For example, an apparatus may be implemented or a method may bepracticed using any number of the aspects set forth herein. In addition,such an apparatus may be implemented or such a method may be practicedusing other structure, functionality, or structure and functionality inaddition to or other than one or more of the aspects set forth herein.Furthermore, an aspect may comprise at least one element of a claim.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any aspect described herein as “exemplary”is not necessarily to be construed as preferred or advantageous overother aspects.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

An Example Wireless Communication System

The techniques described herein may be used for various broadbandwireless communication systems, including communication systems that arebased on an orthogonal multiplexing scheme. Examples of suchcommunication systems include Spatial Division Multiple Access (SDMA),Time Division Multiple Access (TDMA), Orthogonal Frequency DivisionMultiple Access (OFDMA) systems, Single-Carrier Frequency DivisionMultiple Access (SC-FDMA) systems, and so forth. An SDMA system mayutilize sufficiently different directions to simultaneously transmitdata belonging to multiple user terminals. A TDMA system may allowmultiple user terminals to share the same frequency channel by dividingthe transmission signal into different time slots, each time slot beingassigned to different user terminal. An OFDMA system utilizes orthogonalfrequency division multiplexing (OFDM), which is a modulation techniquethat partitions the overall system bandwidth into multiple orthogonalsub-carriers. These sub-carriers may also be called tones, bins, etc.With OFDM, each sub-carrier may be independently modulated with data. AnSC-FDMA system may utilize interleaved FDMA (IFDMA) to transmit onsub-carriers that are distributed across the system bandwidth, localizedFDMA (LFDMA) to transmit on a block of adjacent sub-carriers, orenhanced FDMA (EFDMA) to transmit on multiple blocks of adjacentsub-carriers. In general, modulation symbols are sent in the frequencydomain with OFDM and in the time domain with SC-FDMA.

The teachings herein may be incorporated into (e.g., implemented withinor performed by) a variety of wired or wireless apparatuses (e.g.,nodes). In some aspects a node comprises a wireless node. Such wirelessnode may provide, for example, connectivity for or to a network (e.g., awide area network such as the Internet or a cellular network) via awired or wireless communication link. In some aspects, a wireless nodeimplemented in accordance with the teachings herein may comprise anaccess point or an access terminal.

An access point (“AP”) may comprise, be implemented as, or known asNodeB, Radio Network Controller (“RNC”), eNodeB, Base Station Controller(“BSC”), Base Transceiver Station (“BTS”), Base Station (“BS”),Transceiver Function (“TF”), Radio Router, Radio Transceiver, BasicService Set (“BSS”), Extended Service Set (“ESS”), Radio Base Station(“RBS”), or some other terminology. In some implementations an accesspoint may comprise a set top box kiosk, a media center, or any othersuitable device that is configured to communicate via a wireless orwired medium. According to aspects of the present disclosure, the accesspoint may operate in accordance with the Institute of Electrical andElectronics Engineers (IEEE) 802.11 family of wireless communicationsstandards.

An access terminal (“AT”) may comprise, be implemented as, or known asan access terminal, a subscriber station, a subscriber unit, a mobilestation, a remote station, a remote terminal, a user terminal, a useragent, a user device, user equipment, a user station, or some otherterminology. In some implementations an access terminal may comprise acellular telephone, a cordless telephone, a Session Initiation Protocol(“SIP”) phone, a wireless local loop (“WLL”) station, a personal digitalassistant (“PDA”), a handheld device having wireless connectioncapability, a Station (“STA”), or some other suitable processing deviceconnected to a wireless modem. Accordingly, one or more aspects taughtherein may be incorporated into a phone (e.g., a cellular phone or smartphone), a computer (e.g., a laptop), a portable communication device, aportable computing device (e.g., a personal data assistant), a tablet,an entertainment device (e.g., a music or video device, or a satelliteradio), a television display, a flip-cam, a security video camera, adigital video recorder (DVR), a global positioning system device, or anyother suitable device that is configured to communicate via a wirelessor wired medium. According to aspects of the present disclosure, theaccess terminal may operate in accordance with the IEEE 802.11 family ofwireless communications standards.

FIG. 1 illustrates a multiple-access multiple-input multiple-output(MIMO) system 100 with access points and user terminals. For simplicity,only one access point 110 is shown in FIG. 1. An access point isgenerally a fixed station that communicates with the user terminals andmay also be referred to as a base station or some other terminology. Auser terminal may be fixed or mobile and may also be referred to as amobile station, a wireless device or some other terminology. Accesspoint 110 may communicate with one or more user terminals 120 at anygiven moment on the downlink and uplink. The downlink (i.e., forwardlink) is the communication link from the access point to the userterminals, and the uplink (i.e., reverse link) is the communication linkfrom the user terminals to the access point. A user terminal may alsocommunicate peer-to-peer with another user terminal. A system controller130 couples to and provides coordination and control for the accesspoints.

While portions of the following disclosure will describe user terminals120 capable of communicating via Spatial Division Multiple Access(SDMA), for certain aspects, the user terminals 120 may also includesome user terminals that do not support SDMA. Thus, for such aspects, anAP 110 may be configured to communicate with both SDMA and non-SDMA userterminals. This approach may conveniently allow older versions of userterminals (“legacy” stations) to remain deployed in an enterprise,extending their useful lifetime, while allowing newer SDMA userterminals to be introduced as deemed appropriate.

The system 100 employs multiple transmit and multiple receive antennasfor data transmission on the downlink and uplink. The access point 110is equipped with N_(ap) antennas and represents the multiple-input (MI)for downlink transmissions and the multiple-output (MO) for uplinktransmissions. A set of K selected user terminals 120 collectivelyrepresents the multiple-output for downlink transmissions and themultiple-input for uplink transmissions. For pure SDMA, it is desired tohave N_(ap)≧K≧1 if the data symbol streams for the K user terminals arenot multiplexed in code, frequency or time by some means. K may begreater than N_(ap) if the data symbol streams can be multiplexed usingTDMA technique, different code channels with CDMA, disjoint sets ofsub-bands with OFDM, and so on. Each selected user terminal transmitsuser-specific data to and/or receives user-specific data from the accesspoint. In general, each selected user terminal may be equipped with oneor multiple antennas (i.e., N_(ut)≧1). The K selected user terminals canhave the same or different number of antennas.

The SDMA system 100 may be a time division duplex (TDD) system or afrequency division duplex (FDD) system. For a TDD system, the downlinkand uplink share the same frequency band. For an FDD system, thedownlink and uplink use different frequency bands. MIMO system 100 mayalso utilize a single carrier or multiple carriers for transmission.Each user terminal may be equipped with a single antenna (e.g., in orderto keep costs down) or multiple antennas (e.g., where the additionalcost can be supported). The system 100 may also be a TDMA system if theuser terminals 120 share the same frequency channel by dividingtransmission/reception into different time slots, each time slot beingassigned to different user terminal 120.

According to certain aspects of the present disclosure, one or morecontrol messages may be exchanged between the access point 110 and oneor more of the user terminals 120 for protecting downlink multiusertransmissions over an accompanied wireless medium. The exchanged controlmessages may comprise at least one of Request-to-send (RTS) message(s)or Clear-to-send (CTS) message(s) providing Network Allocation Vector(NAV) information to node(s) not visible to the access point (i.e.,hidden node(s)), wherein the NAV information may comprise an indicationof time for which the medium will be busy. This mechanism may reduce aprobability of collisions during data transmissions.

FIG. 2 illustrates a block diagram of access point 110 and two userterminals 120 m and 120 x in MIMO system 100. The access point 110 isequipped with N_(t) antennas 224 a through 224 t. User terminal 120 m isequipped with N_(ut,m) antennas 252 ma through 252 mu, and user terminal120 x is equipped with N_(ut,x) antennas 252 xa through 252 xu. Theaccess point 110 is a transmitting entity for the downlink and areceiving entity for the uplink. Each user terminal 120 is atransmitting entity for the uplink and a receiving entity for thedownlink. As used herein, a “transmitting entity” is an independentlyoperated apparatus or device capable of transmitting data via a wirelesschannel, and a “receiving entity” is an independently operated apparatusor device capable of receiving data via a wireless channel. In thefollowing description, the subscript “dn” denotes the downlink, thesubscript “up” denotes the uplink, N_(up) user terminals are selectedfor simultaneous transmission on the uplink, N_(dn) user terminals areselected for simultaneous transmission on the downlink, N_(up) may ormay not be equal to N_(dn), and N_(up) and N_(dn) may be static valuesor can change for each scheduling interval. The beam-steering or someother spatial processing technique may be used at the access point anduser terminal.

On the uplink, at each user terminal 120 selected for uplinktransmission, a TX data processor 288 receives traffic data from a datasource 286 and control data from a controller 280. TX data processor 288processes (e.g., encodes, interleaves, and modulates) the traffic datafor the user terminal based on the coding and modulation schemesassociated with the rate selected for the user terminal and provides adata symbol stream. A TX spatial processor 290 performs spatialprocessing on the data symbol stream and provides N_(ut,m) transmitsymbol streams for the N_(ut,m) antennas. Each transmitter unit (TMTR)254 receives and processes (e.g., converts to analog, amplifies,filters, and frequency upconverts) a respective transmit symbol streamto generate an uplink signal. N_(ut,m) transmitter units 254 provideN_(ut,m) uplink signals for transmission from N_(ut,m) antennas 252 tothe access point.

N_(up) user terminals may be scheduled for simultaneous transmission onthe uplink. Each of these user terminals performs spatial processing onits data symbol stream and transmits its set of transmit symbol streamson the uplink to the access point.

At access point 110, N_(ap) antennas 224 a through 224 ap receive theuplink signals from all N_(up) user terminals transmitting on theuplink. Each antenna 224 provides a received signal to a respectivereceiver unit (RCVR) 222. Each receiver unit 222 performs processingcomplementary to that performed by transmitter unit 254 and provides areceived symbol stream. An RX spatial processor 240 performs receiverspatial processing on the N_(ap) received symbol streams from N_(ap)receiver units 222 and provides N_(up) recovered uplink data symbolstreams. The receiver spatial processing is performed in accordance withthe channel correlation matrix inversion (CCMI), minimum mean squareerror (MMSE), soft interference cancellation (SIC), or some othertechnique. Each recovered uplink data symbol stream is an estimate of adata symbol stream transmitted by a respective user terminal. An RX dataprocessor 242 processes (e.g., demodulates, deinterleaves, and decodes)each recovered uplink data symbol stream in accordance with the rateused for that stream to obtain decoded data. The decoded data for eachuser terminal may be provided to a data sink 244 for storage and/or acontroller 230 for further processing.

On the downlink, at access point 110, a TX data processor 210 receivestraffic data from a data source 208 for N_(dn) user terminals scheduledfor downlink transmission, control data from a controller 230, andpossibly other data from a scheduler 234. The various types of data maybe sent on different transport channels. TX data processor 210 processes(e.g., encodes, interleaves, and modulates) the traffic data for eachuser terminal based on the rate selected for that user terminal. TX dataprocessor 210 provides N_(dn) downlink data symbol streams for theN_(dn) user terminals. A TX spatial processor 220 performs spatialprocessing (such as a precoding or beamforming, as described in thepresent disclosure) on the N_(dn) downlink data symbol streams, andprovides N_(ap) transmit symbol streams for the N_(ap) antennas. Eachtransmitter unit 222 receives and processes a respective transmit symbolstream to generate a downlink signal. N_(ap) transmitter units 222providing N_(ap) downlink signals for transmission from N_(ap) antennas224 to the user terminals.

At each user terminal 120, N_(ut,m) antennas 252 receive the N_(ap)downlink signals from access point 110. Each receiver unit 254 processesa received signal from an associated antenna 252 and provides a receivedsymbol stream. An RX spatial processor 260 performs receiver spatialprocessing on N_(ut,m) received symbol streams from N_(ut,m) receiverunits 254 and provides a recovered downlink data symbol stream for theuser terminal. The receiver spatial processing is performed inaccordance with the CCMI, MMSE or some other technique. An RX dataprocessor 270 processes (e.g., demodulates, deinterleaves and decodes)the recovered downlink data symbol stream to obtain decoded data for theuser terminal.

At each user terminal 120, a channel estimator 278 estimates thedownlink channel response and provides downlink channel estimates, whichmay include channel gain estimates, SNR estimates, noise variance and soon. Similarly, a channel estimator 228 estimates the uplink channelresponse and provides uplink channel estimates. Controller 280 for eachuser terminal typically derives the spatial filter matrix for the userterminal based on the downlink channel response matrix H_(dn,m) for thatuser terminal. Controller 230 derives the spatial filter matrix for theaccess point based on the effective uplink channel response matrixH_(up,eff). Controller 280 for each user terminal may send feedbackinformation (e.g., the downlink and/or uplink eigenvectors, eigenvalues,SNR estimates, and so on) to the access point. Controllers 230 and 280also control the operation of various processing units at access point110 and user terminal 120, respectively.

According to certain aspects of the present disclosure, one or morecontrol messages may be exchanged between the transceiver 222 of theaccess point 110 and the transceivers 254 of user terminals 120 in orderto protect following downlink multiuser transmissions. Asaforementioned, the exchanged control messages may comprise at least oneof RTS message(s) or CTS message(s) providing the NAV information to thehidden node(s) of the wireless communication system 100.

FIG. 3 illustrates various components that may be utilized in a wirelessdevice 302 that may be employed within the wireless communication system100. The wireless device 302 is an example of a device that may beconfigured to implement the various methods described herein. Thewireless device 302 may be a base station 104 or a user terminal 106.

The wireless device 302 may include a processor 304 which controlsoperation of the wireless device 302. The processor 304 may also bereferred to as a central processing unit (CPU). Memory 306, which mayinclude both read-only memory (ROM) and random access memory (RAM),provides instructions and data to the processor 304. A portion of thememory 306 may also include non-volatile random access memory (NVRAM).The processor 304 typically performs logical and arithmetic operationsbased on program instructions stored within the memory 306. Theinstructions in the memory 306 may be executable to implement themethods described herein.

The wireless device 302 may also include a housing 308 that may includea transmitter 310 and a receiver 312 to allow transmission and receptionof data between the wireless device 302 and a remote location. Thetransmitter 310 and receiver 312 may be combined into a transceiver 314.A single or a plurality of transmit antennas 316 may be attached to thehousing 308 and electrically coupled to the transceiver 314. Thewireless device 302 may also include (not shown) multiple transmitters,multiple receivers, and multiple transceivers.

The wireless device 302 may also include a signal detector 318 that maybe used in an effort to detect and quantify the level of signalsreceived by the transceiver 314. The signal detector 318 may detect suchsignals as total energy, energy per subcarrier per symbol, powerspectral density and other signals. The wireless device 302 may alsoinclude a digital signal processor (DSP) 320 for use in processingsignals.

According to certain aspects of the present disclosure, one or morecontrol messages may be exchanged between the wireless device 302 andone or more other wireless devices (not shown in FIG. 3) for protectionof following downlink multiuser transmissions. As aforementioned, theexchanged control messages may comprise at least one of RTS message(s)or CTS message(s) providing the NAV information to the hidden node(s) inthe wireless communication system 100 comprising the wireless device302.

The various components of the wireless device 302 may be coupledtogether by a bus system 322, which may include a power bus, a controlsignal bus, and a status signal bus in addition to a data bus.

Those skilled in the art will recognize the techniques described hereinmay be generally applied in systems utilizing any type of multipleaccess schemes, such as SDMA, OFDMA, CDMA, SC-FDMA and combinationsthereof.

In next generation Wireless Local Area Network (WLAN) systems based onthe IEEE 802.11, an access point (AP) (e.g., the access point 110 fromFIG. 1) may transmit data simultaneously to multiple stations (STAs)(e.g., to the user terminals 120 from FIG. 1) using multiusermultiple-input multiple-output (MU-MIMO) transmission scheme based on,for example, Downlink Spatial Division Multiple Access (DL-SDMA).However, prior to such transmission, the AP may transmit arequest-to-send (RTS) message to a plurality of STAs to reserve a mediumfor data communication. The plurality of STAs may be required to respondwith clear-to-send (CTS) messages, if they are to be protected fromother STAs that may not hear the RTS message sent from the AP (i.e.,these other STAs may represent hidden nodes).

Protection Mechanisms For Multiuser Mimo Transmissions

Certain aspects of the present disclosure support multiple mechanismsfor protecting a MU-MIMO transmission, by using appropriate controlmessages exchanged between an AP and supported user STAs beforetransmitting downlink data packets.

In an aspect of the present disclosure, a plurality of STAs addressed inan RTS message transmitted from an AP may be configured tosimultaneously transmit CTS messages. In order to ensure that suchsimultaneously transmitted CTS messages can be correctly decoded at oneor more other STAs (e.g., at hidden nodes), a physical layer waveformthat each of the transmitting STAs produce may need to be substantiallythe same. The process of generating substantially the same waveform ateach of the STAs addressed in the RTS message may involve severalaspects.

In one aspect, it may be required to ensure that all CTS messagestransmitted from all STAs addressed in the RTS message may compriseexactly the same bits. This can be ensured in IEEE 802.11 since only avariable part of CTS message may comprise a destination address, andeach simultaneously transmitted CTS message may be transmitted to thesame AP carrying therefore the same AP's destination address. Further,identical modulation and coding schemes may need to be utilized at eachSTA before over-the-air CTS transmission. In the IEEE 802.11, this maybe ensured since each of the CTS messages may be communicated at a basicrate specified by the AP.

In another aspect, it may be required to ensure that the physical layerprocess of encoding and scrambling before over-the-air CTS transmissiongenerates same bits. In IEEE 802.11, each STA may choose its ownscrambling sequence. Therefore, additional specification may need to beadded so that all the CTS messages generated at the plurality of STAs inresponse to the RTS message may be scrambled using the same scramblingsequence.

FIG. 4 illustrates an example Request-to-send/Clear-to-send (RTS/CTS)based medium reservation protocol 400 with stacked CTS messages forMU-MIMO communication in accordance with certain aspects of the presentdisclosure. An access point (AP) 402 may transmit an RTS message 406comprising a group address that addresses a plurality of STAs. A subsetor all of the STAs (e.g., STAs 404 ₁, 404 ₂, 404 ₃) addressed by the AP402 that can receive a downlink MU-MIMO transmission may thensimultaneously respond with CTS transmissions 408 starting SIFS (shortinter-frame space) time-period 410 after receiving the RTS message 406.Duration fields of the simultaneously transmitted CTS messages 408 maybe set, for example, according to a duration field specified by the RTSmessage 406.

In an aspect of the present disclosure, the AP 402 may specify one ormore parameters in a management message to ensure that the CTS messages408 may comprise a substantially same waveform when being simultaneouslytransmitted from the STAs 4041-4043. The management message may betransmitted from the AP 402 and may be received at the plurality of STAsaddressed by the RTS message 406 prior to simultaneously transmittingthe CTS messages 408. One of the specified parameters in the managementmessage may indicate a scrambling sequence to be applied at each of theSTAs 4041-4043 before transmitting the CTS messages 408. The scramblingsequence applied at all the STAs may be pre-determined (e.g., by theIEEE 802.11 standard body) and stored at each STA to be used whentransmitting a CTS message.

The AP 402 may start downlink MU-MIMO transmissions 412 after the AP 402has received the CTS messages 408 from the STAs 404 ₁-404 ₃. Because ofthe same waveforms, the CTS messages 408 transmitted from the pluralityof STAs may appear as a single physical layer frame at one or more otherSTAs listening to the reserved medium. Therefore, these other STAs maybe able to accurately decode the CTS messages 408, and then properly settheir Network Allocation Vector (NAV) counters according to a durationfield value of the decoded CTS messages.

In an aspect, each of the CTS messages 408 may be transmitted on adifferent spatial stream as specified in the RTS message 406. In anotheraspect, if none of the STAs transmits a CTS message in response to theRTS message 406, then the AP 402 may terminate the protocol 400 and maygo into a back-off state to save power.

In an aspect, multiple STAs (e.g., the STAs 404 ₁-404 ₃) receiving theRTS message 406 may need to know that they are required to reply withCTS messages. A normal action frame may be, for example, utilized fortransmitting the RTS message 406 since the NAV may be set by any dataframe. Transmitting a single RTS message may also have the advantage ofNAV truncation. The AP 402 receiving the CTS messages 408 may not knowwhich STA(s) transmitted it. As long as one of the STAs transmits a CTSmessages, then the AP may assume that there was no collision.

FIG. 5 illustrates example operations 500 that may be performed at anaccess point (e.g., at the access point 402 from FIG. 4) in accordancewith certain aspects of the present disclosure. At 502, the access pointmay transmit a reservation message to a plurality of user stations(e.g., the STAs 404 ₁-404 ₃ from FIG. 4) to reserve a medium for datacommunication. At 504, the access point may receive, on a channel, aplurality of confirmation messages transmitted simultaneously on thechannel from two or more of the user stations in response to thereservation message, wherein the confirmation messages may comprise asubstantially same waveform. At 506, in response to the confirmationmessages, the access point may transmit data over the medium to the twoor more user stations. In an aspect, the data transmitted to the two ormore user stations may comprise a Multi User Multiple Input MultipleOutput Very High Throughput Physical layer convergence procedureProtocol Data Unit (MU-MIMO VHT PPDU).

In an aspect, the reservation message may have a format substantiallythe same as an IEEE 802.11 request-to-send (RTS) message format.Further, each of the simultaneously transmitted confirmation messagesmay have a format substantially the same as an IEEE 802.11 clear-to-send(CTS) message format.

FIG. 6 illustrates example operations 600 that may be performed at auser station (e.g., at one of the STAs 404 ₁-404 ₃ from FIG. 4) inaccordance with certain aspects of the present disclosure. At 602, theuser station of a plurality of user stations may receive a reservationmessage transmitted to the plurality of user stations for reserving amedium for communicating data. At 604, in response to the reservationmessage, the user station may transmit a confirmation messagesimultaneously with transmitting one or more other confirmation messagesfrom one or more of the user stations, wherein all the transmittedconfirmation messages may comprise a substantially same waveformtransmitted on a channel. At 606, the user station may receive datadedicated to that station.

In an aspect, the received reservation message may comprise an RTSmessage including a multicast group address of the user stations. Eachof the user stations may identify, based on the multicast group address,that data to be transmitted are addressed to that particular userstation.

In order for the aforementioned scheme to be effective, it may berequired to assign a group address that captures STAs that will bereceiving MU-MIMO data. It should be noted that if the group addressencompasses too many STAs, then it may not be possible to discern statesat the STAs for which data are to be sent (e.g., the STAs 404 ₁-404 ₃from FIG. 4).

In one aspect of the present disclosure, an AP may construct a uniquegroup address for a given subset of STAs. Then, the AP may communicatethe group address to the subset of STAs using a management message priorto transmitting the RTS message. Each STA from the subset of STAs mayreceive the management frame comprising the unique group address, andmay identify based on the unique group address that data to betransmitted from the AP are addressed to that particular STA.

In another aspect of the present disclosure, the AP may use, forexample, a known hash function to map Media Access Control (MAC)addresses or Association Identifications (IDs) of a desired set of STAsto a group MAC address. The group MAC address may be transmitted by theAP to the set of STAs within a management message prior to transmittingthe RTS message. Then, a STA from the set of STAs receiving themanagement message with the group MAC address may use a reverse mapping(de-map) of the known hash function to determine whether the group MACaddress actually addresses that STA (i.e., to obtain an identificationof that STA). It should be noted that such hash function may need to berestrictive enough to exclude all STAs except those that comprise dataaddressed to them.

In another aspect of the present disclosure, an AP and a plurality ofSTAs may exchange multiple RTS and CTS messages transmittedsequentially. FIG. 7 illustrates an example RTS/CTS based mediumreservation protocol 700 with sequential transmissions of RTS and CTSmessages for MU-MIMO communication in accordance with certain aspects ofthe present disclosure.

As illustrated in FIG. 7, an AP 702 may transmit an RTS message 706 to aSTA 704 ₁. Then, the STA 704 ₁ may respond with a CTS transmission 708that may start SIFS time after receiving the RTS message 706. Afterthat, the AP 702 may transmit an RTS message 710 to another STA 704 ₂,and the STA 704 ₂ may respond with a CTS transmission 712. Followingthis, the AP 702 may transmit an RTS message 714 to a third STA 704 ₃,and the STA 704 ₃ may respond with a CTS transmission 716. Once thecontrol messages 706-716 have been exchanged between the AP 702 and theSTAs 704 ₁, 704 ₂, 704 ₃, the medium may be reserved for all the STAs704 ₁-704 ₃. Then, the AP 702 may start downlink MU-MIMO transmissions718 to the STAs 704 ₁-704 ₃.

FIG. 8 illustrates example operations 800 that may be performed at an AP(e.g., the AP 702 from FIG. 7) in accordance with certain aspects of thepresent disclosure. At 802, the AP may transmit one or more reservationmessages, each of the one or more reservation messages being destined toa different STA of a plurality of STAs to reserve a medium for datacommunication. At 804, the AP may receive one or more confirmationmessages, each of the one or more confirmation messages was transmittedfrom the different STA in response to that reservation message. At 806,in response to the one or more confirmation messages, the AP maytransmit data over the medium to the STAs. In an aspect, the datatransmitted to the STAs may comprise an MU-MIMO VHT PPDU.

In an aspect, the reservation messages may be transmitted sequentially,and the confirmation messages may be transmitted sequentially as well.Further, transmitting each of the reservation messages may immediatelyprecede transmission of a different one of the confirmation messages, asillustrated in FIG. 7.

FIG. 9 illustrates example operations 900 that may be performed at a STAin accordance with certain aspects of the present disclosure. At 902,the STA of a plurality of STAs may receive a reservation message fromone or more reservation messages, each of the one or more reservationmessages being destined to a different one of the STAs for reserving amedium for data communication. At 904, the STA may transmit aconfirmation message in response to the reservation message. At 906, theSTA may receive data dedicated to that STA, the data being transmittedover the medium.

In an aspect, the STA may be configured to count a number of one or moreother confirmation messages previously transmitted from one or moreother STAs of the plurality of STAs to determine when to transmit theconfirmation message. Further, the STA may be able to detect the one ormore other confirmation messages. In one aspect, the confirmationmessage may be transmitted immediately after receiving the reservationmessage. In another aspect, the confirmation message may be transmittedaccording to a scheduled time specified in the reservation message.

FIG. 10 illustrates an example RTS/CTS based medium reservation protocol1000 with a single RTS transmission and sequential transmissions of CTSmessages for protecting MU-MIMO communication in accordance with certainaspects of the present disclosure. As illustrated in FIG. 10, an AP 1002may transmit an RTS message 1006 (e.g., a broadcast message) to aplurality of STAs 1004 ₁, 1004 ₂, 1004 ₃. Then, the STA 1004 ₁ mayrespond with a CTS transmission 1008, followed by a CTS transmission1010 from the STA 1004 ₂, and a CTS transmission 1012 from the STA 1004₃.

Once the control messages 1006, 1008, 1010 and 1012 have been exchangedbetween the AP 1002 and the STAs 1004 ₁-1004 ₃, the medium may bereserved for all the STAs 1004 ₁-1004 ₃. Then, the AP 1002 may startdownlink MU-MIMO transmissions 1014 to the STAs 1004 ₁-1004 ₃.

FIG. 11 illustrates an example RTS/CTS based medium reservation protocol1100 with a single transmission of RTS and a single transmission of CTSmessage for MU-MIMO communication in accordance with certain aspects ofthe present disclosure. As illustrated in FIG. 11, an AP 1102 maytransmit an RTS message 1106 to one of STAs 1104 ₁, 1104 ₂, 1104 ₃(e.g., to the STA 1104 ₁) to reserve a medium for data communication.Then, the STA 1104 ₁ may respond with a CTS transmission 1108. Once theAP 1102 receives the CTS message 1108, the AP may start downlink MU-MIMOtransmissions 1110 to the STAs 1104 ₁-1104 ₃.

The STA 1104 ₁ may be selected by the AP 1102 as a destination of theRTS message 1106. In one aspect, the STA 1104 ₁ may be selected as adestination for a first packet in a queue associated with a trafficbelonging to a class of traffics that won contention to access themedium. In another aspect, the STA 1104 ₁ may be selected based on anumber of collisions during data communication over the mediumassociated with each of the STAs 1104 ₁-1104 ₃. For example, the STA1104 ₁ may be the one that experiences the largest number of collisionsamong the STAs 1104 ₁, 1104 ₂, 1104 ₃.

In yet another aspect of the present disclosure, transmitting one ormore RTS messages for reserving a medium for data communication may beavoided, and an overhead of exchanging control messages may be thereforereduced. FIG. 12 illustrates an example CTS based medium reservationprotocol 1200 with a single transmission of CTS message for MU-MIMOcommunication in accordance with certain aspects of the presentdisclosure.

As illustrated in FIG. 12, an AP 1202 may transmit a confirmationmessage 1206 announcing reservation of a medium for data communicationduring a defined time period. The confirmation message 1206 maycorrespond to a clear-to-send-to-self message, and it may comprise NAVinformation related to the defined time period. Subsequent to thetransmission of confirmation message 1206, data 1208 may be transmittedover the medium to a plurality of STAs (e.g., STAs 1204 ₁, 1204 ₂, 1204₃ illustrated in FIG. 12) during the defined time period.

FIG. 13 illustrates example operations 1300 that may be performed at anAP (e.g., the AP 1202 from FIG. 12) in accordance with certain aspectsof the present disclosure. At 1302, the AP may transmit a confirmationmessage announcing reservation of a medium for data communication duringa time period. At 1304, subsequent to the transmission of confirmationmessage, the AP may transmit data over the medium simultaneously to aplurality of apparatuses during the time period. In an aspect, the datatransmitted simultaneously may comprise an MU-MIMO VHT PPDU.

In an aspect, the confirmation message may have a format substantiallythe same as a clear-to-send-to-self message format. Further, theconfirmation message may comprise NAV information related to the timeperiod.

FIG. 14 illustrates example operations 1400 that may be performed at aSTA in accordance with certain aspects of the present disclosure. At1402, the STA of a plurality of STAs may receive a confirmation messageannouncing reservation of a medium for data communication during a timeperiod. At 1404, the STA may receive data dedicated to that STA, thedata being transmitted over the medium during the time period.

Referring to at least one of the aforementioned example protocols 400,700, 1000, 1100, 1200, certain aspects of the present disclosure supportmethods comprising a transmission by an AP to one or more STAs in a setof receiving STAs. The transmission by the AP may comprise an exchangeof control messages for medium reservation with at least one STA, andtransmitting data from the AP to the one or more STAs in the set ofreceiving STAs. Further, the AP may receive acknowledgments for thetransmitted data from the one or more STAs. The control messages may beexchanged before the data transmission. According to certain aspects,the control messages may comprise at least one of: one or more RTSmessages, or one or more CTS messages.

Each of the RTS messages may comprise at least one of NAV information ora sender address. An indication of the NAV may protect at least one of:a following data transmission time, or a following acknowledgmenttransmission time. Further, each of the RTS messages may comprise a listof addresses of destination STAs, while that RTS message may becompliant with IEEE 802.11 family of wireless communication standards.

Further, in an aspect, each of the RTS messages (e.g., the RTS messages706, 710 and 714 from FIG. 7) may comprise an indication of order inwhich the STAs may be required to reply with CTS transmissions. Inanother aspect, each of the RTS messages may comprise an indication oftime at which one or multiple STAs should reply with one or more CTSmessages.

In an aspect, each of the RTS messages (e.g., the RTS messages 706, 710and 714 from FIG. 7) may comprise a unicast message. In another aspect,a single broadcast or multicast RTS message (e.g., the RTS message 406from FIG. 4) may be transmitted to a plurality of STAs. Further, each ofthe RTS messages (e.g., the RTS messages 706, 710 and 714 from FIG. 7)may comprise a spatial stream allocation to be used by one or more STAsfor the CTS message reply.

In an aspect, each of the RTS messages (e.g., the RTS messages 706, 710and 714 from FIG. 7) may be transmitted on a primary frequency channel.In another aspect, each of the RTS messages may be transmitted on aprimary frequency channel and on one or more secondary channels.

In an aspect, each CTS message may be transmitted on each and only thefrequency channels corresponding to channels of the received RTSmessages. In another aspect, each CTS message may be transmitted from aSTA only if the set of channels where a RTS message is received comprisea primary channel.

In one aspect, data for a STA may not be transmitted if no CTS messageis received from that STA on a primary channel. In another aspect, datafor a STA may not be transmitted if no CTS message is received from thatSTA in at least one of the channels where a RTS message was transmittedfor that STA. Data for each STA may be transmitted using a plurality offrequency channels. These frequency channels may belong to a subset offrequency channels where a CTS message was received from that STA.Alternatively, the frequency channels utilized for data transmission maybelong to a subset of frequency channels where one or more CTS messageswere received from that STA and all other STAs in the plurality of STAs.

Each CTS message may comprise an indication of NAV information. In anaspect, the indication of NAV may be the same one as being receivedwithin a corresponding RTS message. Further, each CTS message may becompliant with IEEE 802.11 family of wireless communication standards.

In one aspect, an AP may be transmitting a single RTS message (e.g., theRTS message 1106 from FIG. 11) destined to a single STA in the set ofreceiving STAs by using, for example, the Enhanced Distributed ChannelAccess (EDCA) protocol for medium access. That single STA may be chosenas a destination for traffic defined as a “primary traffic”. The“primary traffic” may comprise a traffic belonging to a class oftraffics that won contention to access the medium. In another aspect, anAP may be transmitting a single RTS message (e.g., the RTS message 1006from FIG. 10) destined to multiple STAs in a set of receiving STAs byutilizing the EDCA medium access protocol.

The AP may transmit multiple RTS messages (e.g., the RTS messages 706,710 and 714 from FIG. 7) destined to multiple STAs in the set ofreceiving STAs. In one aspect, the multiple RTS messages may betransmitted sequentially to different STAs in the set of receiving STAs.At least the first RTS message (i.e., the RTS message 706) may betransmitted according to the EDCA medium access protocol. The RTSmessages, except the first one, may be transmitted immediately after thereception of a CTS message received as a reply to a previouslytransmitted RTS message. In another aspect, the multiple RTS messagesmay be transmitted simultaneously to different STAs in the set ofreceiving STAs. Further, the simultaneous CTS messages may betransmitted in accordance with MU-MIMO transmission.

Each STA that receives an RTS message may respond with transmitting aCTS message. In one aspect, the CTS message may be transmitted as animmediate reply to the received RTS message. The CTS message in theimmediate reply may be transmitted according to a spatial streamallocation specified in the RTS message. Alternatively, the CTS messagein the immediate reply may be transmitted using a signal which issubstantially the same for all the STAs transmitting simultaneous CTSmessages.

In another aspect, the CTS message may be transmitted after a timespecified in the received RTS message. In yet another aspect, the CTSmessage may be transmitted according to a transmission order received inthe RTS message. In this case, the STA may count a number of precedingCTS transmissions in order to determine when to transmit its CTSmessage. The counting may be performed by detecting the previous CTStransmissions. Further, the CTS message may not be transmitted by a STAif a NAV counter was already set for that STA.

It should be noted that an AP may exclude from a subsequent multi userdata transmission a STA that did not return a CTS message as a responseto an RTS message transmitted from the AP. Further, the AP may includeat least one new STA in a set of receiving STAs, if no CTS message istransmitted by one or more of the STAs in the set of receiving STAs forwhich an RTS message was transmitted. Then, the AP may start exchangingcontrol messages with the at least one new STA.

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrate circuit (ASIC), or processor. Generally,where there are operations illustrated in Figures, those operations mayhave corresponding counterpart means-plus-function components withsimilar numbering. For example, operations 500, 600, 800, 900, 1300 and1400 illustrated in FIGS. 5, 6, 8, 9, 13 and 14 correspond to components500A, 600A, 800A, 900A, 1300A and 1400A illustrated in FIGS. 5A, 6A, 8A,9A, 13A and 14A.

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishingand the like.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover: a, b, c,a-b, a-c, b-c, and a-b-c.

The various operations of methods described above may be performed byany suitable means capable of performing the operations, such as varioushardware and/or software component(s), circuits, and/or module(s).Generally, any operations illustrated in the Figures may be performed bycorresponding functional means capable of performing the operations.

For example, the means for transmitting may comprise a transmitter,e.g., the transmitter 222 from FIG. 2 of the access point 110, thetransmitter 254 from FIG. 2 of the user terminal 120, or the transmitter310 from FIG. 3 of the wireless device 302. The means for receiving maycomprise a receiver, e.g., the receiver 222 from FIG. 2 of the accesspoint 110, the receiver 254 from FIG. 2 of the user terminal 120, or thereceiver 312 from FIG. 3 of the wireless device 302. The means forspecifying may comprise an application specific integrated circuit,e.g., the processor 210 from FIG. 2 of the access point 110, theprocessor 242 from FIG. 2 of the access point 110, the processor 270from FIG. 2 of the user terminal 120, the processor 288 from FIG. 2 ofthe user terminal 120, or the processor 304 from FIG. 3 of the wirelessdevice 302. The means for constructing may comprise an applicationspecific integrated circuit, e.g., the processor 210, the processor 288,or the processor 304. The means for mapping may comprise a mapper, e.g.,the processor 210, the processor 288, or the processor 304. The meansfor applying may comprise an application specific integrated circuit,e.g., the processor 210, the processor 288, or the processor 304. Themeans for scrambling may comprise a scrambler, e.g., the processor 210,the processor 288, or the processor 304. The means for identifying maycomprise an application specific integrated circuit, e.g., the processor210, the processor 242, the processor 270, the processor 288, or theprocessor 304. The means for de-mapping may comprise a de-mapper, e.g.,the processor 242, the processor 270, or the processor 304. The meansfor counting may comprise an application specific integrated circuit,e.g., the processor 210, the processor 242, the processor 270, theprocessor 288, or the processor 304. The means for detecting maycomprise an application specific integrated circuit, e.g., the processor242, the processor 270, or the processor 304. The means for selectingmay comprise an application specific integrated circuit, e.g., theprocessor 210, the processor 288, or the processor 304.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array signal (FPGA) or other programmable logic device(PLD), discrete gate or transistor logic, discrete hardware componentsor any combination thereof designed to perform the functions describedherein. A general purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thepresent disclosure may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in any form of storage medium that is knownin the art. Some examples of storage media that may be used includerandom access memory (RAM), read only memory (ROM), flash memory, EPROMmemory, EEPROM memory, registers, a hard disk, a removable disk, aCD-ROM and so forth. A software module may comprise a singleinstruction, or many instructions, and may be distributed over severaldifferent code segments, among different programs, and across multiplestorage media. A storage medium may be coupled to a processor such thatthe processor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

The functions described may be implemented in hardware, software,firmware, or any combination thereof. If implemented in software, thefunctions may be stored or transmitted over as one or more instructionsor code on a computer-readable medium. Computer-readable media includeboth computer storage media and communication media including any mediumthat facilitates transfer of a computer program from one place toanother. A storage medium may be any available medium that can beaccessed by a computer. By way of example, and not limitation, suchcomputer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that can be used to carry or store desiredprogram code in the form of instructions or data structures and that canbe accessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if the software is transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared (IR), radio, and microwave, thenthe coaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. Disk and disc, as used herein, include compactdisc (CD), laser disc, optical disc, digital versatile disc (DVD),floppy disk, and Bluray® disc where disks usually reproduce datamagnetically, while discs reproduce data optically with lasers. Thus, insome aspects computer-readable media may comprise non-transitorycomputer-readable media (e.g., tangible media). In addition, for otheraspects computer-readable media may comprise transitorycomputer-readable media (e.g., a signal). Combinations of the aboveshould also be included within the scope of computer-readable media.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein. For certain aspects, the computer program product may includepackaging material.

Software or instructions may also be transmitted over a transmissionmedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition oftransmission medium.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

While the foregoing is directed to aspects of the present disclosure,other and further aspects of the disclosure may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

The invention claimed is:
 1. An apparatus for wireless communications,comprising: a transmitter configured to transmit reservation messages,each of the reservation messages being destined to a different apparatusof a plurality of apparatuses to reserve a medium for datacommunication; a circuit configured to select the different apparatusfor transmitting a confirmation message based on that differentapparatus being a destination for a first packet in a queue associatedwith a traffic belonging to a class of traffic that won contention toaccess the medium prior to transmission of the reservation messages; anda receiver configured to receive confirmation messages, wherein each ofthe confirmation messages was transmitted from the different apparatusin response to the reservation message transmitted to the differentapparatus after a time period specified in that reservation message,wherein the transmitter is also configured to transmit, in response tothe confirmation messages, data over the medium to the apparatuses. 2.The apparatus of claim 1, wherein: the confirmation messages arereceived sequentially.
 3. The apparatus of claim 1, wherein: each of thereservation messages has a format of a request-to-send (RTS) message,and each of the confirmation messages has a format of a clear-to-send(CTS) message.
 4. The apparatus of claim 1, wherein each of thereservation messages comprises Network Allocation Vector (NAV)information.
 5. The apparatus of claim 1, wherein the data transmittedto the apparatuses comprise a Multi User Multiple Input Multiple OutputVery High Throughput Physical layer convergence procedure Protocol DataUnit (MU-MIMO VHT PPDU).
 6. An apparatus for wireless communications,comprising: a transmitter configured to transmit reservation messages,each of the reservation messages being destined to a different apparatusof a plurality of apparatuses to reserve a medium for datacommunication; a circuit configured to select the different apparatusfor transmitting a confirmation message based on a number of collisionsduring data communication over the medium associated with each of theplurality of apparatuses prior to transmission of the reservationmessages; and a receiver configured to receive confirmation messages,wherein each of the confirmation messages was transmitted from thedifferent apparatus in response to the reservation message transmittedto the different apparatus after a time period specified in thatreservation message, the different apparatus has a highest number ofcollisions among the numbers of collisions associated with the pluralityof apparatuses, and the transmitter is also configured to transmit, inresponse to the confirmation messages, data over the medium to theapparatuses.
 7. A method for wireless communications, comprising:transmitting reservation messages, each of the reservation messagesbeing destined to a different apparatus of a plurality of apparatuses toreserve a medium for data communication; selecting the differentapparatus for transmitting a confirmation message based on thatapparatus being a destination for a first packet in a queue associatedwith a traffic belonging to a class of traffic that won contention toaccess the medium prior to transmission of the reservation messages;receiving confirmation messages, wherein each of the confirmationmessages was transmitted from the different apparatus in response to thereservation message transmitted to the different apparatus after a timeperiod specified in that reservation message; and transmitting, inresponse to the confirmation messages, data over the medium to theapparatuses.
 8. The method of claim 7, wherein: the confirmationmessages are received sequentially.
 9. The method of claim 7, wherein:each of the reservation messages has a format of a request-to-send (RTS)message, and each of the confirmation messages has a format of aclear-to-send (CTS) message.
 10. The method of claim 7, wherein each ofthe reservation messages comprises Network Allocation Vector (NAV)information.
 11. The method of claim 7, wherein the data transmitted tothe apparatuses comprise a Multi User Multiple Input Multiple OutputVery High Throughput Physical layer convergence procedure Protocol DataUnit (MU-MIMO VHT PPDU).
 12. A method for wireless communications,comprising: transmitting reservation messages, each of the reservationmessages being destined to a different apparatus of a plurality ofapparatuses to reserve a medium for data communication; selecting thedifferent apparatus for transmitting a confirmation message based on anumber of collisions during data communication over the mediumassociated with each of the plurality of apparatuses prior totransmission of the reservation messages, wherein the differentapparatus has a highest number of collisions among the numbers ofcollisions associated with the plurality of apparatuses; receivingconfirmation messages, wherein each of the confirmation messages wastransmitted from the different apparatus in response to the reservationmessage transmitted to the different apparatus after a time periodspecified in that reservation message; and transmitting, in response tothe confirmation messages, data over the medium to the apparatuses. 13.An apparatus for wireless communications, comprising: means fortransmitting reservation messages, each of the reservation messagesbeing destined to a different apparatus of a plurality of apparatuses toreserve a medium for data communication; means for selecting thedifferent apparatus for transmitting a confirmation message based onthat apparatus being a destination for a first packet in a queueassociated with a traffic belonging to a class of traffic that woncontention to access the medium prior to transmission of the reservationmessages; and means for receiving confirmation messages, wherein each ofthe confirmation messages was transmitted from the different apparatusin response to the reservation message transmitted to the differentapparatus after a time period specified in that reservation message,wherein the means for transmitting is further configured to transmit, inresponse to the confirmation messages, data over the medium to theapparatuses.
 14. The apparatus of claim 13, wherein: the confirmationmessages are received sequentially.
 15. The apparatus of claim 13,wherein: each of the reservation messages has a format of arequest-to-send (RTS) message, and each of the confirmation messages hasa format of a clear-to-send (CTS) message.
 16. The apparatus of claim13, wherein each of the reservation messages comprises NetworkAllocation Vector (NAV) information.
 17. The apparatus of claim 13,wherein the data transmitted to the apparatuses comprise a Multi UserMultiple Input Multiple Output Very High Throughput Physical layerconvergence procedure Protocol Data Unit (MU-MIMO VHT PPDU).
 18. Anapparatus for wireless communications, comprising: means fortransmitting reservation messages, each of the reservation messagesbeing destined to a different apparatus of a plurality of apparatuses toreserve a medium for data communication; means for selecting thedifferent apparatus for transmitting a confirmation message based on anumber of collisions during data communication over the mediumassociated with each of the plurality of apparatuses prior totransmission of the reservation messages; and means for receivingconfirmation messages, wherein each of the confirmation messages wastransmitted from the different apparatus in response to the reservationmessage transmitted to the different apparatus after a time periodspecified in that reservation message; wherein the different apparatushas a highest number of collisions among the numbers of collisionsassociated with the plurality of apparatuses, and the means fortransmitting is further configured to transmit, in response to theconfirmation messages, data over the medium to the apparatuses.
 19. Acomputer-program product for wireless communications, comprising acomputer-readable device encoded with instructions executable to:transmit reservation messages, each of the reservation messages beingdestined to a different apparatus of a plurality of apparatuses toreserve a medium for data communication; select the different apparatusfor transmitting a confirmation message based on that apparatus being adestination for a first packet in a queue associated with a trafficbelonging to a class of traffic that won contention to access the mediumprior to transmission of the reservation messages; receive confirmationmessages, wherein each of the confirmation messages was transmitted fromthe different apparatus in response to the reservation messagetransmitted to the different apparatus after a time period specified inthat reservation message; and transmit, in response to the confirmationmessages, data over the medium to the apparatuses.
 20. An access point,comprising: at least one antenna; a transmitter configured to transmitreservation messages via the at least one antenna, each of thereservation messages being destined to a different access terminal of aplurality of access terminals to reserve a medium for datacommunication; a circuit configured to select the different accessterminal for transmitting a confirmation message based on that accessterminal being a destination for a first packet in a queue associatedwith a traffic belonging to a class of traffic that won contention toaccess the medium prior to transmission of the reservation messages; anda receiver configured to receive confirmation messages via the at leastone antenna, wherein each of the confirmation messages was transmittedfrom the different access terminal in response to the reservationmessage transmitted to the different access terminal after a time periodspecified in that reservation message, and the transmitter is alsoconfigured to transmit, via the at least one antenna in response to theconfirmation messages, data over the medium to the access terminals. 21.An apparatus for wireless communications, comprising: a receiverconfigured to receive, at the apparatus of a plurality of apparatuses, areservation message from a plurality of reservation messages, each ofthe reservation messages being destined to a different one of theplurality of apparatuses for reserving a medium for data communicationand having an indication of a transmission order for one or moreapparatuses of the plurality of apparatuses to transmit confirmationmessages; a circuit configured to count a number of one or moreconfirmation messages transmitted from one or more other apparatuses ofthe plurality of apparatuses to determine when to transmit aconfirmation message; and a transmitter configured to transmit theconfirmation message in response to the reservation message and based onthe determination and the transmission order, wherein the receiver isalso configured to receive data dedicated to the apparatus, the databeing transmitted over the medium.
 22. The apparatus of claim 21,wherein the circuit is also configured to detect the one or moreconfirmation messages.
 23. The apparatus of claim 21, wherein: thereservation message has a format of a request-to-send (RTS) message, andthe confirmation message has a format of a clear-to-send (CTS) message.24. The apparatus of claim 21, wherein the confirmation messagecomprises Network Allocation Vector (NAV) information specified in thereceived reservation message.
 25. A method for wireless communications,comprising: receiving, at an apparatus of a plurality of apparatuses, areservation message from a plurality of reservation messages, each ofthe reservation messages being destined to a different one of theplurality of apparatuses for reserving a medium for data communicationand having an indication of a transmission order for one or moreapparatuses of the plurality of apparatuses to transmit confirmationmessages; counting a number of one or more confirmation messagestransmitted from one or more other apparatuses of the plurality ofapparatuses to determine when to transmit a confirmation message basedon the transmission order; transmitting the confirmation message inresponse to the reservation message and based on the determination; andreceiving data dedicated to the apparatus, the data being transmittedover the medium.
 26. The method of claim 25, further comprising:detecting the one or more confirmation messages.
 27. The method of claim25, wherein: the reservation message has a format of a request-to-send(RTS) message, and the confirmation message has a format of aclear-to-send (CTS) message.
 28. The method of claim 25, wherein theconfirmation message comprises Network Allocation Vector (NAV)information specified in the received reservation message.
 29. Anapparatus for wireless communications, comprising: means for receiving,at the apparatus of a plurality of apparatuses, a reservation messagefrom a plurality of reservation messages, each of the reservationmessages being destined to a different one of the plurality ofapparatuses for reserving a medium for data communication and having anindication of a transmission order for one or more apparatuses of theplurality of apparatuses to transmit confirmation messages; means forcounting a number of one or more confirmation messages transmitted fromone or more other apparatuses of the plurality of apparatuses todetermine when to transmit a confirmation message based on thetransmission order; means for transmitting the confirmation message inresponse to the reservation message and based on the determination,wherein the means for receiving is further configured to receive datadedicated to the apparatus, the data being transmitted over the medium.30. The apparatus of claim 29, further comprising: means for detectingthe one or more confirmation messages.
 31. The apparatus of claim 29,wherein: the reservation message has a format of a request-to-send (RTS)message, and the confirmation message has a format of a clear-to-send(CTS) message.
 32. The apparatus of claim 29, wherein the confirmationmessage comprises Network Allocation Vector (NAV) information specifiedin the received reservation message.
 33. A computer-program product forwireless communications, comprising a computer-readable device encodedwith instructions executable to: receive, at an apparatus of a pluralityof apparatuses, a reservation message from a plurality of reservationmessages, each of the reservation messages being destined to a differentone of the plurality of apparatuses for reserving a medium for datacommunication and having an indication of a transmission order for oneor more apparatuses of the plurality of apparatuses to transmitconfirmation messages; count a number of one or more confirmationmessages transmitted from one or more other apparatuses of the pluralityof apparatuses to determine when to transmit a confirmation messagebased on the transmission order; transmit the confirmation message inresponse to the reservation message and based on the determination; andreceive data dedicated to the apparatus, the data being transmitted overthe medium.
 34. An access terminal, comprising: at least one antenna; areceiver configured to receive, at the access terminal of a plurality ofaccess terminals via the at least one antenna, a reservation messagefrom a plurality of reservation messages, each of the reservationmessages being destined to a different one of the plurality of accessterminals for reserving a medium for data communication and having anindication of a transmission order for one or more access terminals ofthe plurality of access terminals to transmit confirmation messages; acircuit configured to count a number of one or more confirmationmessages transmitted from one or more other apparatuses of the pluralityof access terminals to determine when to transmit a confirmation messagebased on the transmission order; a transmitter configured to transmit,via the at least one antenna, the confirmation message in response tothe reservation message and based on the determination, wherein thereceiver is also configured to receive data dedicated to the accessterminal via the at least one antenna, the data being transmitted overthe medium.